Update metadata for ch.protonmail.protonmail-bridge

[razzeee]

This PR updates the metadata to improve discoverability and user experience for Proton Mail Bridge.

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🏷️ Keywords

- email encryption
- secure email client
- proton mail bridge
- imap integration
- end to end encryption

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Generated by Metadata Bot 🤖

[flathubbot]

🚧 Test build enqueued.

[flathubbot]

🚧 Started test build.

[flathubbot]

✅ Test build succeeded. To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/230495/ch.protonmail.protonmail-bridge.flatpakref

Built for x86_64 architecture.